Pressure transducers have been miniaturized and improved to a point where precise readings of pressure are converted to an analog voltage in a device that is very reliable and rugged. In addition, modern devices are quite small and relatively inexpensive. Accordingly, such devices are used extensively in a wide variety of applications. The analog output voltage can easily be applied to a display or indicator of any desired nature or it can be used to control other devices in response to the pressure conditions. For example, if the pressure readout is for an altimeter application, altitude can be displayed or the analog voltage coupled to the controls of an aircraft. In underwater applications, the pressure can be converted to depth indications and/or control.
In transducer specifications there are three major characteristics: offset, sensitivity, and span. Span refers to the range of voltages representing the pressures. If, for example, a particular fluid transducer covers a pressure range of 0 to 100 psia, and has an output of 2.5 to 12.5 volts, the span is expressed as 10 volts and 100 pounds. This yields 10 pounds per volt sensitivity. Since zero psia is represented by 2.5 volts, the offset is 2.5 volts.
Commercial transducers are available in a wide selection of characteristics. Typically, the span and sensitivity characteristics are not subject to much variation, these being largely established in the device at manufacture. The offset characteristic is the most subject to drift or change. Such changes can occur as either short term, usually ambient condition related, errors or long term, drift-related, errors. since these offset errors affect the accuracy of readings at any pressure, it is essential that they be compensated as much as possible. In the prior art this was done by actual calibration, repeated as often as was regarded as necessary and practical. In effect, accuracy was compromised to whatever degree that could be tolerated in order to make a system practicable. It would be desirable to automate or mechanize calibration so that it can be indulged to whatever extent is deemed useful for accurate readings.